Disclosures and filing the return (part 5)
Published 17 December 2025
© Crown copyright 2025
This publication is licensed under the terms of the Open Government Licence v3.0 except where otherwise stated. To view this licence, visit nationalarchives.gov.uk/doc/open-government-licence/version/3 or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email: psi@nationalarchives.gov.uk.
Where we have identified any third party copyright information you will need to obtain permission from the copyright holders concerned.
This publication is available at https://www.gov.uk/government/publications/help-with-imported-hybrid-mismatches-gfc16/disclosures-and-filing-the-return-part-5
In this part we provide best practice recommendations for disclosing a Self Assessment counteraction. Our recommendations are based on best practice approaches observed from customers. Best practice may differ depending on the facts and circumstances of the transaction. UK businesses will need to apply a degree of proportionality and materiality to their compliance work. In our experience, questions about the disclosure are resolved promptly when record keeping includes:
- a clear disclosure and compliance audit trail
- compliance steps taken to complete the analysis are recorded
- information relied upon and how it was used is retained
Where your analysis identifies a counteraction, a standardised disclosure is required in boxes B65 and B70 of form CT600B. The disclosure should both identify the existence of and the quantum of counteractions. Read HMRC guidance for help to accurately complete the CT600B — Supplementary pages CT600B: controlled foreign companies and foreign permanent establishment exemptions, hybrid and other mismatches.
HMRC recommends including a whitespace note, or other narrative schedule disclosure, in the supporting computation of the CT600B. This is not mandatory but it is helpful to contextualise the counteraction being disclosed. Use this note to:
- identify which chapters of Part 6A the disclosed counteractions relate to (whether under Chapter 11 or another Chapter)
- disclose the respective amounts of any counteraction
- include details of the analysis undertaken and summarise the conclusions made in arriving at the counteraction amounts
HMRC may request additional information in line with standard CTSA record keeping requirements. Read CH11200 - Record Keeping: What records must be kept: Income tax, capital gains tax and corporation tax general requirements. We expect that contemporaneous records are retained. These should provide HMRC with sufficient information as reasonably required to explain and substantiate the filed counteraction. Further detail on the specific imported hybrid mismatch records to retain are set out in Evidence and documentation (part 6).
Where your Self Assessment determines no counteraction outcome under Chapter 11 — you are not required to disclose this when filing your tax return. For a no counteraction outcome it’s best to prepare and retain the information and analysis the same way as those that result in a counteraction. This ensures supporting evidence is available that the filed return is correct and complete.